Production of manganese



0% 1956 c. CAROSELLA 2,766,197

PRODUCTION OF MANGANESE Filed July 30, 1953 Carbonaceons Material Man anese Ore a -A||o in Metal or Sui hur g l wh ere desired p FURNACE -1 Manganese Slag Alloy Fe Reidue 2 Cell-Feed Anolyfe Manganse Meial r COOR 7 Filfrate Mixed Magnesium -Manganese- I Ammonium Sulfate Crystals INVENTOR ATTORNEY PRODUCTION OF MANGANESE Michael C. Carosella, Niagara Falls, N. Y., assignor to Union Carbide and Carbon Corporation, a corporation of New York Application July 30, 1953, Serial No. 371,285

4 Claims. (Cl. 204-103) The present invention relates to a process for the elec trolytic production of manganese metal from solutions containing manganese and ammonium salts, and to the preparation of said solutions from manganese-bearing materials.

Heretofore, it has been the practice to obtain solutions for the electrowinning of manganese from reduced manganese-containing ores. In such processes the ore containing manganese in the form of manganese dioxide is treated in the solid phase, in the presence on a reducing agent, to obtain a product containing manganous oxide which is then leached with a mineral acid and treated with ammonia and other agents to remove the ore residue and other impurities and to produce high purity manganese and ammonium salt solutions which are suitable for cell feed in the electrowinning of highly pure metallic manganese. Such former processes, although .they provided solutions which when electrolyzed resulted in the production of suitable manganese metal, were very complex and costly due to equipment and treatment required to separate the metallic impurities fromthe reduced ore.

It is, therefore, the main object of the present invention to reduce the complexity of the former processes for producing electrolytic metallic manganese from solutions prepared from reduced manganese ores.

Another object is to provide a process for obtaining solutions for the production of electrolytic metallic mangauese wherein the manganese-containing material employed to produce such solutions has a very low metallic impurity content thereby greatly reducing the complexity of the solution forming and purification steps.

Other aims and advantages of the present invention will be apparent from the following description and appended claims.

For some time manganese-bearing slags have been produced as by-products of many smelting operations wherein manganese in the reduced state and an alloy are produced. An example of such a process is the method for the production of ferromanganese wherein manganese ore, containing manganese in the form of manganese dioxide, is smelted with carbon and possibly some iron to yield ferromanganese and a manganese slag containing manganese in the form of manganous oxide (bi-valent state).

Slags which have been produced as by-products of this and similar smelting operations have not been exceedingly high in manganese content, the manganese metal content usually being about by weight of the slag. Such slags were commonly thrown away due to their low manganese values and the high cost required to advantageously extract these values. Such slags may be employed in accordance with this invention as source material for the preparation of solutions suitable for the electrowinning of manganese.

It has been found that, by varying the conditions under which the smelting operation is performed, the percentage of manganese in the resulting slag can be varied over Wide ranges. It has also been found that manganese slags t6 Patent produced from these smelting operations are low in metal impurity content, most of the metal impurities originally associated with the ore such as iron, cobalt, nickel, copper, etc., becoming associated with the alloy during the smelting operation thereby leaving a slag containing only minor amounts of such impurities.

In accordance with the process of the present invention a manganese-bearing ore, is first smelted with a reducing agent, such as coke, to produce a manganese alloy such as ferromanganese, and a manganese slag containing manganese in the form of manganous oxide (bivalent state). The conditions under which this smelting operation is performed are preferably such as to produce a slag having a manganese content in excess of approximately 20% by weight.

Therefore, it can be seen that the former smelting process has been modified to the extent that slags containing a higher manganese and low metallic impurity content are produced, which slag can serve as a source of manganese for a cyclic process for the electrowinning of manganese.

The single figure of the drawing is a flow sheet illustrating the steps of a process embodying the invention wherein manganese ore is smelted to produce a slag which serves as a source of manganese for a cyclic process for the electrowinning of manganese.

As shown in the drawing, a manganese ore and reducing agent, such as coke, are smelted in furnace 1 under conditions suitable to produce a manganese alloy and a manganese slag.

The manganese slag so obtained is leached with a mineral acid, such as sulphuric or hydrochloric acid, the major portion of which is obtained from anolyte formed at and recycled from the later electrowinning step and the remainder from makeup acid. The anolyte may be purified, where necessary, to remove magnesium before recycling. This step is indicated as box 2 in the flow sheet. To the leach slurry so formed, a source of sulphide ions, such as ammonium sulphide, may then be added when, in an unusual case, it is necessary to make up for a deficiency of sulphide ions in the slag. This addition Will ordinarily not be required since the smelting of most manganese ores will produce a manganese slag sufiiciently high in sulphur content to easily accomplish the sulphide precipitation of metallic impurities from the solution. Alternately, where it is desired to insure that the manganese slag formed from the smelting operation contains a sutficient quantity of sulphur, a source of sulphur may be added to the furnace charge in step 1 to accomplish that result.

The pH of the leach slurry obtained in the step just described is then adjusted to approximately 4.0 to 7.5 by the addition of ammonia. The resulting pulp is filtered to remove the residue which consists largely of silica, alumina, carbon, and sulphides of the objectionable metal impurities, such as copper, lead, nickel, cobalt and zinc. If a suificient amount of sulphide ions is present in the solution, a large part of the iron impurity will also beprecipitated as ferrous sulphide. This step is illustrated as box 3 of the flow sheet. The resulting filtrate is treated with hydrogen peroxide, or equivalent oxidizing agent, to oxidize the iron to ferric hydroxide. This oxidizing step is shown as box 4 of the flow sheet. The iron precipitate (ferric hydroxide) so obtained is removed from the solution, as is illustrated by box 5 of the flow sheet. Sulphur dioxide is added to the filtrate. The resulting solution is introduced into the cathode compartment of a diaphragm electrolytic cell as cell feed.

The cell for the electrowinning of manganese from such solutions may employ any suitable electrodes. When sulphate solutions are used anodes of 99% lead-1% silver alloy may be employed while graphite anodes may be employed when chloride solutions are used.

Electrolysis of sulphate solutions in the cell results in the formation of high purity manganese metal at the cathode and the mineral acid and some manganese dioxide at the anode. This step is illustrated in box 6 of the flow sheet.

It has been found that very satisfactory metal is obtained at satisfactory current efiiciencies when the cathode current density is in the range of approximately 15-80 amperes per square foot (and the anode current density is in the range of approximately 30-160 amperes per square foot).

When a sulphate bath is used and magnesium is present in the starting material, the anolyte obtained from the electrowinning step is cooled to a temperature less than the cell operating temperature whereupon mixed magnesiurn-manganese-ammonium salt crystals are formed. The cooler is shown as step 7 in the drawing. These crystals are removed from the solution whereupon the solution is recycled to the leaching step. The crystal removal step is illustrated by box 8 of the flow sheet.

In the process of the present invention, when the pH of the leach slurry is adjusted to about 4.0 to 7.5, the sulphide ions, carried into the leach slurry with the manganese slag, as well as the sulphide ions which may have been introduced to make up for any deficiency in the leach slurry, react with the metal impurities, such as copper, lead, nickel, cobalt, zinc, and most of the iron to produce sulphide ions of these metal impurities. In order to provide electrolyte solutions substantially free from these metal impurities, it is imperative that an amount of sulphide ions suflicient to combine with substantially all of the metal impurities derived from the manganese slag be present in the leaching step. In the very rare case where the manganese slag does not have this sufficient quantity of sulphide ions initially associated with it, it will be necessary to make up for the deficiency by adding a source of sulphide ion to the leaching step prior to the pH adjustment of the leach slurry. The addition of ammonium sulphide, or suitable equivalent, to the leach slurry will satisfy this deficiency of sulphide ions. If a sufiicient amount of sulphide ions is not present in the leach slurry all of the heavy metal impurities will not be removed from the leach slurry in the form of sulphide precipitates and would, therefore, carry through the entire cycle and result in a marked drop in current efiiciency in the electrowinning step.

The use of a magnesium removal step in the process of the present invention is made necessary by the fact that, if not removed in a planned step, complex magnesium salts will crystallize out in the first sufliciently cool part of the cycle thereby causing serious operating difiiculties. The removal is, therefore, included where made necessary by the magnesium content of the slag employed. The entire quantity of anolyte need not be treated in the magnesium purification step, but the treatment of merely a portion of the anolyte will ordinarily sufiice to keep the magnesium concentration sufficiently low to prevent such a buildup in the cycle.

An example of the present invention setting forth quantitative values at every step is as follows:

Forty-five hundred pounds of manganese ore (49.0% Mn, 5.1% Fe, 5.4% SiOz, 4.1% A1203, 0.14% P), and 920 parts of coke were smelted in an electric arc furnace to produce 2370 pounds of metal (consisting principally of manganese and a small amount of phosphorus, copper, nickel, and cobalt) and 1030 pounds of manganese slag -(containing 38.4% Mn, 0.34% Fe, 24.6% SiOz, 19.4% A1203, 0.003% Cu and 0.001%CO-i-Ni). Five hundred fifty pounds of this manganese slag was ground to finer than 200 mesh and leached to a pH of 4.4 with 950 gallons of recycled anolyte together with make-up sulphuric acid, The leach liquor analyzed 11.9 g./l. Mn, 44 g./1. H2804, 120 g./l. (NH4)2SO4. The pH of the liquor was then adjusted to 6.6 by the addition of 11.0 pounds of ammonia. The resultant slurry was filtered in a filter press to yield a filtrate containing 32.2 g./l. of manganese. The manganese extraction from the slag was therefore 74.6%. The filtrate was treated with cc. of 30% H202 to cause oxidation and precipitation of contained iron values as ferric hydroxide. The resultant slurry was again filtered in a filter press and 1.0 g./l. S02 was added to the filtrate to form cell feed.

The cell feed solution was fed into the catholyte compartment of a diaphragm compartment cell and electrolyzed under the following conditions:

Catholyte pH 8.5, Temperature 40 C.

Cathode current density 45' amps/ft Voltage 5.3 volts.

Anode composition 99% Pb=1% Ag. Cathode composition Stainless steel. Current efiiciency 65%.

An adherent sheet of manganese metal was deposited at the cathode and was found to be of high purity 0on taining in excess of 99.9% Mn, 0.032% S and only traces of Fe, Ni and Co.

The anolyte was treated to remove contained magnesium and then recycled to theleaching step to leach a further portion of manganese slag.

The cyclic process of the present invention may of course be practiced without the magnesium removal steps by directly recycling the anolyte to the leaching step. 7 In the specific examples given hereinabove to illustrate the steps of the present invention, no deficiency of sulphide ions existed in the leach slurry, and, hence, the addition of a source of such ions was not required.

This is a continuation in part of application Serial No. 291,535 filed June 3, 1952, now abandoned.

I claim:

1. A process for recovering manganese from its ore materials to produce a manganese-rich alloy fraction and a substantially pure metallic manganese fraction which comprises smelting said manganese ore material with a carbonaceous reducing agent to produce a manganeserich alloy and a manganese-bearing slag, said allow containing at least the major portion of metallic impurities originally present in said ore material and the manganese content of said slag being substantially all in the bivalent state; leaching the slag so produced with a mineral acid; providing in the resulting leach liquid a quantity of sulphide ions suflicient to combine with metallic impurities present therein; separating the metallic sulphide precipitates so-formed from said solution; and electrolysing said solution for deposition of substantially pure manganese therefrom. 2. A process for recovering manganese from its ore materails to produce a manganese-rich alloy fraction and a substantially pure metallic manganese fraction which comprises smelting said manganese ore material with sulphur and a carbonaceous reducing agent to produce a manganese-rich alloy and a manganese-bearing slag, said alloy containing at least the major portion of metallic impurities originally present in said ore material, said slag containing manganese substantially all in the bivalent state and having associated therewith contained metallic impurities and a sulphur content sufficient to produce, upon leaching, a quantity of sulphide ions suflicient to combine with substantially all of said contained metallic impurities; leaching the slag so produced with a mineral acid; separating the metallic sulphide precipitates soformed from said solution; and electrolyzing said solution for deposition of substantially pure metallic manganese therefrom.

3. A process for recovering manganese from its ore materials to produce a manganese-rich alloy fraction and a substantially pure metallic manganese fraction which comprises smelting said manganese ore material with sulphur and a carbonaceous reducing agent to produce a manganese-rich alloy and a manganese-bearing slag, said alloy containing at least the major portion of metallic impurities originally present in said ore material, said slag containing manganese substantially all in the bivalent state and having associated therewith contained metallic impurities and a sulphur content sufiicient to produce, upon leaching, a quantity of sulphide ions sufiicient to combine With a substantial portion of said contained metallic impurities; leaching the slag so produced with a mineral acid; separating the metallic sulphide precipitates so-formed from said solution; and electrolyzing said solution for deposition of substantially pure metallic manganese therefrom.

4. A process for recovering manganese from its ore materials to produce a manganese-rich alloy fraction and a substantially pure metallic manganese fraction which comprises smelting said manganese ore material with a carbonaceous reducing agent to produce a manganeserich alloy and a manganese-bearing slag, said alloy containing at least the major portion of metallic impurities originally present in said ore material and the manganese content of said slag being substantially all in the bivalent state; leaching the slag so produced with a mineral acid to provide a manganese-bearing solution; providing in said manganese-bearing solution a quantity of sulphide ions suflicient to combine with the metallic impurities present therein to form metallic sulphide precipitates and a quantity of oxidizing agent suflicient to react with any remaining iron impurities present to form iron oxide precipitate; separating said impurity precipitates from the as-formed solution; and elec-trolyzing said solution for deposition of substantially pure metallic manganese therefrom.

References Cited in the file of this patent UNITED STATES PATENTS Hunter Jan. 8, 1946 Mitchell et a1 Mar. 11, 1947 OTHER REFERENCES 

1. A PROCESS FOR RECOVERING MANGANESE FROM ITS ORE MATERIALS TO PRODUCE A MANGANESE-RICH ALLOY FRACTION AND A SUBSTANTIALLY PURE METALLIC MANGANESE FRACTION WHICH COMPRISES SMELTING SAID MANGANESE ORE MATERIAL WITH A CARBONACEOUS REDUCING AGENT TO PRODUCE A MANGANESERICH ALLOY AND A MANGANESE-BEARING SLAG, SAID ALLOW CONTAINING AT LEAST THE MAJOR PORTION OF METALLIC IMPURITIES ORIGINALLY PRESENT IN SAID ORE MATERIAL AND THE MANGANESE CONTENT OF SAID SLAG BEING SUBSTANTIALLY ALL IN THE BIVALENT STATE; LEACHING THE SLAG SO PRODUCED WITH A MINERAL ACID; PROVIDING IN THE RESULTING LEACH LIQUID A QUANTITY OF SULPHIDE IONS SUFFICIENT TO COMBINE WITH METALLIC IMPURITIES PRESENT THEREIN; SEPARATING THE METALLIC SULPHIDE PRECIPITATES SO-FORMED FROM SAID SOLUTION; AND ELECTROLYZING SAID SOLUTION FOR DEPOSITION OF SUBSTANTIALLY PURE MANGANESE THEREFROM. 